Voltage control apparatus



Sept 28, 1943. R. B. HULL VOLTAGE CONTROL APPARATUS RII ll. W

Sepf. 28, 1943. R B HULL 2,330,429

` VOLTAGE;l CONTROL @,PPARATUS Filed Feb. 13, 1942 2 Sheets-Sheet 2ATTOF( NEY- Patented Sept. 28, 1943 VOLTAGE CONTROL APPARATUS RaoulHull, Anderson, Ind., assignor to General Motors Corporation, Detroit,Mich., a corl poration of Delaware Application February 13, 1942, SerialNo. 430,769

2 Claims.

This invention relates to apparatus for testing the perfomance ofpower-shaft-driven devices, at various speeds. The device to be testedis driven by a variable speed electric motor which is quickly brought torest after the test by resistance loading its amature thus providing adynamic brake. It is an object of the invention to provide a system ofcontrol of the speed of the electric motor which permits the use of amanually operated control apparatus known hereinafter as a controlmonitor and having provisions for varying speed without the use ofelectrical contactors in response to movement of a control handle, andhaving means for causing dynamic braking to become 'operative inresponse to the movement of the control handle to zero speed position.

To control the speed oi' the electric motor I make use of a feature ofthe system of my copending application No. 382,789 filed March 1l, 1941,which discloses a system for providing a variable D. C. voltage withoutthe use of a rheostat having electrical contactors. In this system thecontrolled D. C. voltage is obtained by rectification of an A. C.voltage through the use of rectifier tubes of the thyratron type. Bymeans of adjustable reactors an infinitely variable control ofthe phaserelation between the grid voltage and the cathode'voltage of the tubesis obtained, over a wide range. By varying this phase relation, thepoint in the A. C. wave in the anode circuitat which the tubes fire canbe varied. Consequently the D. C. output voltage obtained by recticationof alternating current can be varied over a'wide range, the increment oivariation being as small or as large as desired.

In'the present invention, the control monitor handle actuates the coresof the adjustable reactors to control the motor speed and also effectsthe application of rectified A. C. voltage to the armature the electricmotor when the handle is moved away from zero speed position and theopening of a normally closed resistor load circuit of the motorarmature. Conversely, when the handle is returned to zero speedposition, the application of rectiiied A. C. voltage to the armatureceases and the amature resistance loading is reestablished to brakerotation of the armature.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearlyshown.

' In the drawings:

Fig. l vis a wiring diagram of an embodiment of the present invention.

Fig. 2 is a plan view (with the cover removed) of a manually operatedcontrol monitor for varying the angle of phase shift between the gridvoltage and the cathode voltage of the rectifier tubes.

Fig. 3 is a side view thereof with cover and one of the reactors insection. l

Fig. 4 is a sectional view on line 4-4 of Fig. 2.

Fig. 5 is a sectional view taken on lines 5 5 of Fig. 3.

Fig. 6 is a sectional View (enlarged) taken on line 6-8 of Fig. 2.

Fig. '7 is a fragmentary view showing the manner of hinging certainparts of the brake of the control monitor.

Fig. 8 is a diagram showing the manner iny transformer for supplyinganode current to two grid controlled rectifier tubes and 80a forfuliwave rectification. The ends of transformer secondary 82 areconnected by wires 85a, 88a with contacts 85 and 3B, respectively, of arelay 40 having movable contacts 4| and 42 for connecting contacts 8land 88 respectively with other stationary contacts 81 and 88 connected,respectively, with anodes 82 and 82a of tubes 80 and a. Movable contacts4I and 42 are insulated from each other and-are connected by a rod 48with an amature 44 normally down against a stop 48 and attractedupwardly by a coil 48 connected by wire 2B and 44a with the tap2'l oftransformer secondary 82. Tap 28 of secondary 82 is connected by wires28 and 50a with a thermal switch l0 having a bimetal blade 48 carrying acontact 41 for engaging a contact 48l connected with wire |20, andhaving a heater coil Il connected with secondary 256 of a transformer 55by wires 25Go and 256D. The thermal switch l0 is so constructed that,when the instrument is at room temperature, the normally separatedcontacts 41 and 48 will engage in about one minute after the switch 22is closed. As will be apparent later the purpose of this is to permitthe rectiner tubes BB and 60a to be heated before becoming connectedwith secondary 82 of transformer 80. Tubes 80 and 38a are preferablytype IPG-17 thyratron tubes.

The closing of switch 22, connects wires 20 and 2| with primary coil 54of auxiliary transformer 55 having secondary coils 56, 51 and 256. Thefunction of secondary 5B is to supply the necessary power to thecathodes or heaters 8| and 6 la of the rectier tubes 60 and 80a havinggrids 63 and @Banconnected respectively with ilxed resistances 64 andI64a, the purpose of which is to l limit the grid current.

The function of secondary 51 of transformer 55 is to supply power to thephase shifting circuits (indicated by lines of medium width in Fig. "1)comprising the apparatus 10 hereinafter called the control monitor. Itsfunction is to vvary the phase relation oi the grid voltage with respmto cathode voltagewithin certain lilmits. Since the phase-shiftingmethod of grid control is used, an excess of voltage may be applied tothe monitor 1li. Monitor 10 comprises two variable inductive reactors 12and 14 of the movable core type which cooperate with two adjustablereslstances 1| and 13 connected in bridge tothe secondary 51 oi thephase shifting voltage transformer 55. Resistences 1| and 13 may bemounted on a. panel which supports the tubes and transformers. Theseresistances are adjusted to balance the tubes 60 and 60a. By means ofresistors 1| and 13 the limits of the angle of phase shift of gridvoltage with respect tocathode voltage are set, thus determining therange within which lies the point in the A. C. wave in the anode circuitatl which the tube lires; and at the same time balancing the anodecurrent through the tubes. Wire 15 connects an end or transformersecondary 51 with reactor coil 12 having a connection at 18 withresistor 1| and with a wire 11 leading to resistance 3 and grid S3. Wire18 connts anend of transformer secondary 571 with reactor coil 14-having a'connection at 19 'with resistor 13 andA connected by wire awith resistance 86a and grid 63a. -Wire 8| connects wire 18 withresistor 13. Wire 82 connects Wire 18 with resistor 1|.

One side of the rectified D. C. line includes wire 03v (heavy line)connected with the center taps of 4the transformer secondaries 58 and51, a swinging choke 84, wire 85 and armature A of motor M whose speedis to be controlled. The other side of the rectied D. C. line includeswire 33 connectedwith armature A and with the center tap of secondary 32of transformer` 3Q. Wire con nects wire 88 with a filter condenser e@carracci-e across the D. C. output wires 85 and. et. 'Condenserv 90reduces the ripple and raises the output voltage. Variablebleeder-resistor 9|, mnnected in parallel with condenser 90 to bleed thesame, operates to absorb any high inverse voltage surges from anyhighlyv inductive power device such as motor M which is connected withwires 85 and 88. The function of the swinging choke Y84 is to protectthe rectifier tubes 80 and 60a since the peak charging current of thecondenser 30 willrch a value in excess of the rated capacity of thesetubes.

By change the inductive reactance in the bridge circuits which isaccomplished by movingv the cores 12a and'14a in or out vo1' the reactorcoils 12. and 14, a variation oi' the phase relation of the grid voltagewith respeotto cathode voltage is obtained over a wide range thusproviding 'an accurate control over the output of the' rectier tubesfrom zero load to full load depending on the limits set by theresistances 1| and 13. In the diagram Fig. 8, distance horizontally onthe line -C represents time and the distances vervitally representvoltage, The curve ABC represents one-halt of a. full wave ofalternating current, the distance AC being 180 or the time of one-halfcycle of alternating current. The distance from the curve ABC to thebase line AC represents instantaneous A. C. voltage applied to thetubes. The line DEF represents, vectorially, an angle of 180, EG or EGrepresents grid voltage and two conditions of phase shift which mayexist. When'the .reactor'cores 12a 'and 14a are located so as to occupyall of the central portion withinvthe reactor coils 12 and 14, the gridvoltage line G will coincide with line EF denoting that grid voltage isata180 phase displacement with respect to the alternating currentvoltage represented by ABC. At C, this voltage is zero; therefore nooutput current will be passed by the tubes 60 and 60a, When vthe reactorcores 14 and 14a are pulled part-way out, the grid voltage changes phasefrom DEF or 180 to angle DEG. GF represents voltage drop across thereactors 12 and 14; and GD represents voltage drop across the resistors1| and 13. In every instance the vectors EG and EG' represent the valueof the voltages impressed on the grids. Ihis means that the tubes Siland`6|la will begin to pass current at point H on alternating currentvoltage wave ABC. The shaded portion under the line HC represents theoutput from the tubes 60 and 60a. When the reactor cores 12a and 14ahave been nearly wlth' drawn from the reactor coils 12 and 14 the phaserelation between grid voltage andcathode voltage changes to the angleDEG. GF 'is the reactor voltage drop and GD is! the resistor voltagedrop. This means that the tubes 60 and 60a begin to pass current atpoint H on the alternating current voltage curve ABC. I'he shadedportion.

beneath the line HBC represents the output of the tubes. Itis thereforeapparent that the Withdrawal of the cores from the reactors changesconditions from one wherein the tubes do not pass current at any timeduring the alternating cur-v rent wave to a condition wherein the tubespass current at all times during the wave. Consequently, the rectiedoutput voltage is increased frcsm zero to the maximum during thewithdrawal of the reactor cores and is reduced as the cores are movedback into the reactor coils.

On the right hand side of Fig. l is shown a lever me for turning a shaft|0| carrying a .brake drum H32 engaged by brake liningmembers |03 and|04 (Fig. 6) attached, respectively, to brake bands |05 and lil@ whichare hingedly connected at |01 and are urgedvtoward the drum by a springI08-surrounding a screw lili? passing through the bandsl |05 and let andengaging anut ||0. 'I'he extension lia of the band |05 carries a contact||2 for engaging a. contact connected with magnet coil H3 of a relay|25. When the handle |00 is rotated clockwise, the contact ||2 willengage the Acontact in order to connect a magnet coil ll3'with wires 2liand 29. The coil ||3 will be energized and will attract upwardly asolenoid armature ||4 ixmilatingly connected by a frame H5 with contactsH8 and"|2|. lli and l |2 are separated and ||3 is deenergized contact H8engages contacts ||1 and ||8 and contact |2| is separated from contacts|22 and The mechanical connections (not shown in Fig. l) between thehandle |00 and the reactor cores 12a and 14a will be explained in detaillater in connection with the description of Figs. 2 to 6. Forthepresent, it is sumcient to state that when the handle |00 is movedcounterclockwise, the

cores 72a and Ha are-beingwlthdrawn from the When contacts assess coils12 and 14,; and. conversely when the handle |44 is moved clockwise, thecores are being moved into the coils. Therefore, when the handle |44 ismoved counterclockwise, the output voltage increases; and, when thehandle is moved clockwise, the output voltage decreases. While thehandle |44 is being moved counterclockwise the switch contacts 'and ||2are separated due to the face that band extension |44 moves against astop |44b due to the frictional drag of drum |42 and due tothe action ofspring I44c.

Therefore, magnet coil ||4 is disconnected from transformer secondary 32and contact H4 engages contacts H1 and |l4 of relay |24. As soon asthermal switch 44 closes coil 44 of relay 44 will be connected withsecondary 32 and the amature 44 will move upwardly to connect contacts4| and 42 with contacts 34-41 and 34-34 and thus to render tubes 44 and44A effective to cause a rectified D. C. voltage to be applied to motorarmature A and indicated by the heavy lines in Fig. i. At the same timea rectined D. C. voltage, which remains substantially constant isapplied to motor field F as indicated by the medium heavy dash lines inFig. 1. When switch 44 closes while contact |I4 engages contacts ||1 andH4, the magnet coil 244 of relay 244 is connected with the taps 21 and24 of secondary 32 by wire 244a connected with wire 24 and by wire 244be connected with wire |24. Armature 244 of relay 244 rises to causecontacts 24| and 242 (insulatingly supported by the amature) to engagecontacts 234-231 and 234-244 thereby connecting secondary 32 withrectifier tubes 244 and v2444 through wires 234a and 234s and circuitsrespectively including resistances 243 and anodes 242 and resistances243a and anodes 242a. Cathodes 24| and 24Ia are connected by wires 244aand 244|: with secondary 244 of transformer 44. Secondary center tap 241is `connected by wire 241s with motor field I". Resistance 244,connected across field l'I and parallellng a ripple-smoothing condensery244, is a bleeder resistance which improves the smoothing of the D. C.ripple and keeps the peak voltage from reacting upon the tubes 244 and244a.

Cathodes -24| and 24|a are heated by the current iiowing fromtransformer secondary 244. Cathode 4| and lla are heated by the currentI flowing from transformer secondary 44, the censhorted through anadjustable resistance |24.- thereby motor M to stop quickly.

'nie construction of the control monitor wm now be described in detailwith reference to Figs. 3 to '1. The shaft which supports the' handle|44 is rotatably supported by plates |34 |4| attached to a base plate|32. Plate |32 supports a bracket |33 which supports pairs of angle bars|34. Each pair of angle bars |44 an e'x- 4ternal magnetizable core |34of the 12 and 14. Within each external core |34 is located a reactorcoil 12 or 14 surrounding ay non-inag-v netizable tube |34. Each tubereceives an adjust` able core 12a or 14a. As shown in Fig. 2 the cores12a and 14a are connected by a cross pin |31 which is connected by links|34 and a pin |34 with a lever |44 pivoted upon a rod |4| supported bythe plates |34 and |3|. The right end of lever |44 pivotalLv` supports aroller |42 for engaging a cam |43 attached to shaft |4|. The roller |42is urged toward the cam |43 and the cores 12a or 14a are urgeddownwardly by a spring |44 attached at its lower end to a screw |44fixed to theA base |32 andattached at its upper end to a screw |44 fixedto the lever |44. The cam |43' is so shaped asto increase thesensitivity of the control monitor as the handle'l44 is movedcounterclockwise from zerospeed position.

The apparatus is housed by a case or cover |44 attached to the base.This case is provided with I a slot |4| through which the handle- |44`aextends.

ter tap of which is connected with cathode shields I 4|S and 4|Sa.

When the' handle |44 of the control monitor is moved clockwise to causethe speed of the motor M to decrease, the spring |44C resists thetendency of extension |44a to move toward the left due to the frictionalengagement of drum |42 (rotating clockwise) with bands |44 and |44 untilthe handle |44 has arrived at such position that a stop lug |42b(provided by plate |42a adjustably secured to drum |42 by a screw |42cpassing through an arcuate slot |42d in platev |42a and threaded into atapped hole in the drum |42) engages band |44. Thus further movement ofhandle |44 in a clockwise direction causes the contact ||2 to engagecontact HI against the force exerted by spring |44c. Then magnet coil||3 of relay |24 is connected with secondary 32 and contact i4 is raisedabove contacts I1 and H4 and contact |2| is raised into engagement withcontacts |22 and |24. Then the rectifier tubes 44-44a and 244-244a aredisconnected and the impression of rectified current upon the motorwindings ceases; and the armature A is A portion of the case adjacentthe slot' |4| may be provided with a scale of graduation showing thedifferent speeds of the generator being tested corresponding topositions of the handle. The movement of the handle |44 is limited byproviding the shaft |4| with'a cross pin |44 (Fig. 4) the ends of whichkmaystrike a stop pin |44 attached to the plate |3 I.

The handle |44 is frictionally held'A in any position in which it may beset. For this' purpose the shaft |4| drives a brake disc |44' engagedlby brake shoes |4| and |42 attached to brake bands |43 and |44 which arehingedly1 connected at |44 and which are urged towards each other by aspring |44 surrounding a screw |41 passing through ends of the bands |43and |44 and threadedly engaging a nut |44. The band |43 has a straightextension |43a attached by a screw' |43b to base |32. The brake drum |44is intcgral with the brake drum |42, also shown diagrammatically in Fig.l.

As shown in Fig. 3, the plate |3| supports a bracket |14 carrying anonconducting bushing |1| supporting a screw |12 carrying the contactill. 'I'he screw receives a nut |14 for attaching the screw |12 to thebushing |1|. The screw also receives a nut |14 for securing a wirel (not(shown) to the screw |12. The brake band extension |44a supports anon-conducting bushing |44 through which extends a screw |4| carryingthe contact H2. Screw |4i receives a nut |42 for securing the screw tothe band |44. 'Screw |4| receives a nut |43 for attaching a wire (notshown) to the screw |4I. Plate |3| provides the stop member |44b locatedin the path of movement of the brake band extension |44, therebylimiting the extent of separation oi' the contacts ||2 and when thehandle |44 is moved counterclockwise in Figs. l and 3.

The manner of hingedly connecting the parts of each pair of brake bandswill now be described with reference to Fig.,7, which is drawn doublethe scale of Figs. 5 and 6.` One of the brake bands such as |44, isprovided witha slot |44 and the other brake band member, such as |08, isprovided with a head |9| separatedby a narrow neck- |92 from theremainder of the band. Slot |90 is slightly, longer than the width ofthe head.

|9|so `that the head may be passed through the slot when the head is 90from the position shown in Fig. 7. r The neck |92, which is slightlygreater in width than the thickness of the band member |08, isreceivedby the intermediate enlarged portion |9001 the slot |90 when themember |06 is turned linto the position shown in Fig. 7, after its head|9| has been passed through the slot |90.

The band members |83 and |64 are hingedly connectedy in asimilarfashion. The cover or case |50 supportsthe indicator lamp |52 as shownin Fig. 3, and may also support the switch 29.

Fig. 6 shows clearly the adjustable plate |02a having .the lug |02b forengaging the band exftension |05a as the handle |00 approaches zeroposition. To adjust the location of lug |02b, the screw |02c is loosenedand the plate |02a is rotated about the axis o! shaft the bifurcations|||2e ofthe plate bearing on the hub of the drum |02.l The plate |02a isretained in adjusted po- -sition by tightening the screw |020 whichpasses |02d and ls threaded through the arcuate slot into the drum |02.y

When the system is used to control the speed of'a-l H. P.,y 220 v. D. C.motor having a normal speed of 3600rR. P. M., satisfactory results areobtained when the electrical dimensions of the various units are asfollows:-

The secondaries are provided with taps for voltage changes and thevalues of voltage given above are mammums.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is tobe understood that other formsmight be adopted, all coming within the scope of 5 the claims whichfollow.

What is claimed is as follows:

1. Apparatus for controlling the speed of a D. C. .motor having anarmature and iield, an A. C. source, means connected with the A. C.

source for supplying a rectied current to the motor eld, means connectedwith the A. C. source for supplying a rectiiid current to the motorarmature, apparatus for varying the voltage of the rectified currentsupplied to the armature and including a variable inductive reactorhaving a movable core, and a controller having a movable operatinghandle and means operated therebyfor moving the core and having meansresponsive to movement of the handle to low voltage position for causingthe means which supplies rectled current to the motor armature to berendered inoperative and for causing the motor armature to be resistanceloaded.

2. Apparatus for. controlling the speed of a D. C. motor having anamature and eld, an A. C. source, means connected with the A. C. sourcefor supplying a rectified current to the motory field, means connectedwith the A. C.

source for supplying a rectified current to the motor armature,apparatus for varying the voltage of the rectied current supplied to thearmature and including a variable inductive reactor having a movablecore, arelay having a magnet coil and armature and two switchescontrolled by the armature, onebeing normally closed and the othernormally open when the magnet coil is deenergized, and a controllerhaving a movable operating handleland means operated thereby for movingthe core andfhaving a normaliv open switch controlling the circuit ofsaid relay magnet coil and means responsive to movement of the handle tolow voltage position for closing said switch o! the controller wherebythe normally closed switch and normally open switch oi.' the relay arerespectively open and closed, means responsive to the opening of thenormally closed relay switch for rendering inoperative the means whichsupplies rectified current to the motor armature, and an armatureresistance load established by the -closing of the normally open relayswitch.

RAQUEL B. HULL.

